A power amplifier (PA) is an important component in electronic equipment. It may amplify power of a weak electrical signal, so as to meet demands of transportation and transmission. It is expected in an ideal case that an output signal of a PA is obtained by ideally amplifying an input signal. However, for a physical reason, nonlinearity is often introduced into a PA, that is, besides the input signal being amplified, some extra unneeded signals are also added. In order to realize ideal amplification, such nonlinearity of the PA must be compensated and corrected.
Digital predistortion (DPD) technique is effective technical means for precompensating for nonlinearity of electronic equipment. Adaptive predistortion technique may adaptively adjust a coefficient of a predistorter according to a fed back output signal of a PA, so as to realize precompensation.
FIG. 1 is a schematic diagram of a part of the structure of a digital predistortion apparatus in the prior art. As shown in FIG. 1, the digital predistortion apparatus may include a digital predistortion unit 101, a signal transmitting unit 102, a feedback unit 103, a digital filter 104, and a predistortion coefficient unit 105, etc;
wherein, the signal transmitting unit 102 may include a digital analog converter (DAC) 1021, a quadrature modulator (QMOD) 1022, a variable gain amplifier (VGA) 1023, and a high power amplifier (HPA) 1024, etc. The feedback unit 103 may include a quadrature demodulator (QDMOD) 1031, and an analog digital converter (ADC) 1032, etc. The digital filter 104 may include a digital bandpass filer (DBPF), and a digital high pass filter (DHPF), etc. And the predistortion coefficient unit 105 may include a cost function calculating unit 1051, and a coefficient updating unit 1052, etc.
And on the other hand, as the increase of bandwidths of transmission signals, a PA further presents a “memory effect”, that is, the current output signals of the PA are not only related to the current input signals, but also to previous input signals. And its amplitude and phase characteristics present “getting fat”. FIGS. 2 and 3 show an amplitude (AM) characteristic and a phase (PM) characteristic of a power amplifier containing a memory effect, respectively. Nonlinearity and memory effect will destroy a transmission signal, affect signal reception quality and interfere with signals of neighboring channels. Therefore, they need to be overcome and compensated.
It should be noted that the above description of the background is merely provided for clear and complete explanation of the present application and for easy understanding by those skilled in the art. And it should not be understood that the above technical solution is known to those skilled in the art as it is described in the background of the present application.